docs: readme for queue

Author: yeoshuheng

src/dataStructures/queue/README.md

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+# Queue
+
+A queue is a linear data structure that restricts the order in which operations can be performed on its elements.
+
+### Operation Orders
+
+![Queue](https://media.geeksforgeeks.org/wp-content/cdn-uploads/20221213113312/Queue-Data-Structures.png)
+
+*Source: GeeksForGeeks*
+
+Queue follows a FIFO, first in first out order.
+This means the earliest element
+added to the stack is the one operations are conducted on first.
+
+A [stack](../stack/README.md) is a queue with operations conducted in an opposite manner.
+
+## Analysis
+
+As a queue only interacts with either the first or last element regardless during its operations,
+it only needs to keep the pointers of the two element at hand, which is constantly updated as more
+elements are removed / added. This allows stack operations to only incur a *O(1)* time complexity.
+
+## Notes
+
+### Stack vs Queues
+
+Stack and queues only differ in terms of operation order, you should aim to use a stack when
+you want the most recent elements to be operated on.
+Some situations where a stack would work well include build redo / undo systems and backtracking problems.
+
+On the other hand, a queue allows you to operate on elements that enter first. Some situations where
+this would be useful include Breadth First Search algorithms and task / resource allocation systems.
+
+### Arrays vs Linked List
+It is worth noting that queues can be implemented with either a array or with a [linked list](../linkedList/README.md).
+In the context of ordered operations, the lookup is only restricted to the first element.
+
+Hence, there is not much advantage in using a array, which only has a better lookup speed (*O(1)* time complexity)
+to implement a queue. Especially when using a linked list to construct your queue
+would allow you to grow or shrink the queue as you wish.
+
+### Queue Variants
+
+These are some variants of queue that are commonly used.
+
+#### Double Ended Queue (Deque)
+
+![Deque](https://media.geeksforgeeks.org/wp-content/uploads/anod.png)
+
+*Source: GeeksForGeeks*
+
+Deque is a variant of queue where elements can be removed or added from the head and tail of the queue.
+Deque could come in handy when trying to solve sliding window problems.
+
+However, it is important to note that when implementing a deque, unlike a queue, you would require a doubly linked list.
+
+#### Monotonic Queue
+
+This is a variant of queue where elements within the queue are either strictly increasing or decreasing.
+Monotonic queues are often implemented with a deque.
+
+Within a increasing monotonic queue, any element that is smaller than the current minimum is removed.
+Within a decreasing monotonic queue, any element that is larger than the current maximum is removed.
+
+It is worth mentioning that the most elements added to the monotonic queue would always be in a 
+increasing / decreasing order,
+hence, we only need to compare down the monotonic queue from the back when adding new elements.
+